Absorbent sheet products in rolled form find extensive use in modern society. Rolls of toilet paper, towels such as household (kitchen) towels or hand towels etc. are staple items of commerce.
Rolls of absorbent sheet product for home use (e.g. toilet paper) typically consist of a continuous web of absorbent material that is spirally wound around a prefabricated core made of a stiff material such as cardboard or glued paper. The core defines an axial hollow passageway, which is centrally positioned relative to the roll and extends from one edge of the roll to the other edge. The axial hollow passageway enables the consumer to easily mount the roll on the spindle of a roll holder. However, the core is expensive, requires storage space and additional manual handling. Furthermore, the core remains after use of the absorbent sheet product, thus increasing the risk of clogging sewage systems.
To address these concerns, “coreless” rolls and rolls with water-soluble cores have been developed. Among the most important properties of these products are their resistance to collapsing and their flexibility/elasticity.
“Collapsing” refers to the phenomenon occurring when the absorbent sheet product constituting the first inner turns of the roll (i.e. the turns forming the axial hollow passageway at winding start) cannot be stably maintained such that an axial hollow passageway is clearly defined.
Coreless rolls are generally associated with an increased risk of “collapsing”. Collapsing typically occurs in the manufacture process of coreless rolls when the temporary core is extracted after completing the winding, or during storage and transport of the finished product. As a consequence of collapsing, it may become difficult to mount the roll on the spindle of a roll holder. Furthermore, collapsing generally creates a feeling of decreased product quality among consumers.
A “flexible” roll offers the benefit that it can be provided in a compressed form, which requires less space during storage and transport. As a result, storage and transport costs can be significantly reduced. The roll can be returned from its compressed (oval) form to the uncompressed (cylindrical) form by applying pressure along the longer diameter of the compressed (oval) form, i.e. perpendicular to the axis of the roll.
However, the absorbent sheet product constituting the first inner roll turns must be stably maintained when the roll is returned from the compressed form to the uncompressed form. That is, the axial hollow passageway must open itself and be clearly defined when the roll is returned to the cylindrical form. The roll must hence exhibit flexibility and a certain level of elasticity, which means that the roll can be returned to its cylindrical form while reopening the axial hollow passageway in a clearly defined manner. This requires the first inner turns to newly and stably maintain the axial hollow passageway. As a result, there should be no visible difference in appearance between a roll that has been returned from the compressed form to the uncompressed form and a roll that has not been previously subjected to compression.
Previous attempts at applying a binder to the first inner turns to assist in stably maintaining the axial hollow passageway produced a stiff core which consists of a number of turns of glued elongated material. Such a core lacks flexibility and shows low elasticity. As a result, after the roll has been compressed, it is difficult to reopen the axial hollow passageway in a manner leading to a well-defined axial hollow passageway.
Moreover, the first inner turns of elongated material (i.e. the turns of elongated material forming the core) are cohesively maintained together by the binder. The delamination force needed for separating the first inner turns is generally greater than the tear strength of the elongated absorbent material. It is hence difficult to separate the first inner turns without tearing apart the elongated absorbent material on which the binder is applied. As a result, it is not possible to use the elongated absorbent material on its whole length, e.g. up to the last sheet.
Additional attempts at applying an aqueous adhesive to the first inner turns was very difficult to dry, because the paper material generally has good absorbency towards liquids, and thus the water contained in the adhesive and thus the finished roll-shaped product is never completely dried. As a result, the paper material onto which the adhesive is applied exhibits some stickiness, which creates an unpleasant feeling among consumers.
In spite of the previous attempts there is still an unmet desire for a coreless roll of an absorbent sheet product which combines superior resistance to collapsing with improved flexibility and elasticity. It is also desirable for a coreless roll of an absorbent sheet product to be usable over essentially its whole length (i.e. essentially up to the last sheet) and to prevent sewage systems from clogging up. Additionally, it is desirable for a coreless roll of an absorbent sheet product to be capable of being provided in the compressed form, wherein, after the roll has been compressed, the axial hollow passageway can be reopened in a manner leading to a well-defined axial hollow passageway.